Electrical bushing assembly having resilient means enclosed within sealing means

ABSTRACT

Mechanical stress-relieving means for high-voltage bushings. Resilient means is located between a first member attached to the bushing lead tube and a second member which is adjacent to the upper weather casing of the bushing. Different rates of thermal expansion of the bushing components are compensated for by the resilient means. Bushing dielectric seal between the first and second members is provided by either a gasket member or a semiflexible band.

United States 1 1 Hildenbrand et al.

1 1 Sept. 18, 1973 ELECTRICAL BUSHING ASSEMBLY HAVING RESILIENT MEANS ENCLOSED WITIIIN SEALING MEANS [75] Inventors: Jerry L. Hilden brand; Loren B.

Wagenaar, both of Muncie, Ind.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Apr. 27, 1972 [21] Appl. No.: 247,951

[52] US. Cl. 174/12 B111, 174/31 R [51] Int. Cl. 1101b 17/26 -[58] Field of Search 174/11 811, 12 BH,

174/14 BH, 15 BH,16 BH, 18, 31 R, 75 F, 152 R, 153 R, 167

[56] References Cited UNITED STATES PATENTS 2,135,321 11/1938 Brandt 174/12 BH x 2,228,440 1/1941 Chubbuck 174/12 BH x 2,257,652

9/1941 Rorden 174/12 BH Primary Examiner-Laramie E. Askin Attorney-A. T. Stratton et a1.

[57] ABSTRACT Mechanical stress-relieving means for high-voltage bushings. Resilient means is located between a first member attached to the bushing lead tube and a second member which is adjacent to the upper weather casing of the bushing. Different rates of thermal expansion of the bushing components are compensated for by the resilient means. Bushing dielectric seal between the first and second members is provided by either a gasket member or a semi-flexible band.

4 Claims, 4 Drawing Figures ELECTRICAL EIJSI-IING ASSEMBLY HAVING RESILIEN'I MEANS ENCLOSED WITI-IIN SEALING MEANS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical bushings and, more specifically, to mechanical stressrelieving means for power transformer electrical bushing assemblies.

2. Description of the Prior Art Substantial increases during recent years in transmission line voltages have made it necessary to construct electrical bushings which are capable of withstanding the electrical stresses associated with the higher voltages. Generally, bushings can usually be constructed to operate satisfactorily at higher voltages by increasing the size of the bushing. However, with the high transmission voltages now being tested and proposed for the future, the size of the bushing required exceeds practi cal limits. Standard construction techniques are not practical in constructing bushings for these extremely high voltages. The size of the bushing becomes so large that mechanical strength problems exist and the space required to mount the bushing becomes excessive.

Due to the relatively long length of the bushing components and the difference in the coefficients of thermal expansion, it is necessary to have some means provided in the bushing for relieving stresses which may develop between these components. Spring loading the bushing casing structure and lead tube has been useful in eliminating component stresses. A description of such an arrangement is disclosed in US. Pat. No. 2,853,538 which is assigned to the same assignee as this invention. Although useful at lower voltages, the prior art arrangements increase the overall length of the bushing and are not as desirable for higher voltage bushings. The spring loading assembly is contained within the oil expansion cap whichadds to the overall length of the bushing.

In some high-voltage applications,'oil expansion caps are not ordinarily required. Oil expansion may be compensated for by an oil reservoir connected with the oil contained within the bushing. Or, the bushing may not be sealed and the oil therein allowed to communicate with the oil in its associated electrical apparatus. However, since difierences in thermal expansions still exist, a stress-relieving means must still be used. Consequently, with the prior art arrangements which have stress-relieving means contained within the expansion cap, the bushing is unnecessarily large when oil expansion provided by the expansion cap is not required.

Therefore, it is desirable, and it is an object of this invention, to provide an electrical bushing assembly which contains stress-relieving means constructed and positioned to minimize the size of the bushing.

SUMMARY OF THE INVENTION New and useful electrical bushing assemblies are disclosed wherein stress-relieving means are provided which allow the physical size of the bushing to be as small as practicable. In a first embodiment of this invention, the stress-relieving means includes a cap located near the top of the lead tube, a cup located between the cap and the upper casing of the bushing, and

a resilient means and a gasket located between the cup and the cap. The resilient means places the proper forces on the bushing components and allows relative movement between the casing structure and the lead tube to reduce mechanical stresses. The gasket seals the bushing dielectric from its surroundings. In another arrangement of the first embodiment, a flexible band is attached between the cap and the cup to seal the bushing dielectric from its surroundings.

In a second embodiment of this invention, the stressrelieving means is positioned near the bushing support member and includes resilient means located inside a circular channel member. The circular channel member telescopes with the bushing support member to relieve the stresses. A flexible band is attached to the circular channel and to the bushing support member to seal the bushing dielectric from its surroundings. In another arrangement of the second embodiment, the resilient means is located between a slotted ring member and the bushing support member. The bushing support member telescopes into the slot of the ring member.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawing, in which:

- FIG. 1 is an elevational view, partly in section, of an electrical bushing having stress-relieving means near an end of the bushing and constructed according to an embodiment of this invention;

FIG. 2 is a partial sectional view of another embodiment of the electrical bushing shown in FIG. ll;

FIG. 3 is a partial elevational view, partly in section, of an electrical bushing having stress-relieving means near the center of the bushing and constructed according to an embodiment of this invention; and

FIG. 4 is a partial view of another embodiment of the electrical bushing shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all Figures ofthe drawing.

Referring now to the drawing, and FIG. l in particular, there is shown an electrical bushing assembly constructed according to one embodiment of this invention. The lead tube It) is cylindrically shaped and has ends 12 and I4 and a longitudinal axis extending between the ends ]l2 and M. Bushing leads, which are not illustrated, may be attached to the lead tube covers 116 and 18 for providing connections between the bushing and its associated electrical circuits.

A casing means, including an upper casing 20, a lower casing 22, and a bushing support member 2d, is concentrically disposed around the lead tube It). The bushing is normally attached to an electrical apparatus enclosure by the support flange 26. The casings 20 and 22 may be constructed of any suitable material, such as porcelain or an epoxy resin. Usually, the bushing support member 24 is constructed of a metallic material whtn the bushing is relatively large.

The lower portion of the casing 22 is attached to the end M of the lead tube It) by a suitable means. The bushing support member 2% is positioned between the casings 20 and 22 and is efiectively connected to the end M of the lead tube 10 through the lower casing 22.

. The upper casing 20 is attached to the end 12 of the lead tube 10 by a stress-relieving means 28.

The stress-relieving means 28 comprises a cap 30 having a substantially circular shape with an opening 32 therein through which the end 12 of the lead tube extends. The cap 30 is secured to the lead tube 10 by the spanner nut 34 which is threadably engaged with the lead tube 10.

The cap 30 includesslots, such as the slot 36, into which the upper ends of the coil springs 38 are placed. The number of coil springs 38 and the force provided thereby depends on the size and type of the bushing assembly. A substantially circular cup 40 having an opening 42 in the bottom portion 44 of the cup 40 has slots, such as the slot 46, into which the lower ends of the coil springs 38 are placed.

The cup 40 contains an outwardly extending flange 48 which is positioned substantially between the cap 30 and the upper casing 20. A suitable sealing means, such as the gasket 50, provides a fluid-tight seal between the flange 48 and the upper casing 20. This prevents leakage of the fluid dielectric 52 which is illustrated as oil although other dielectrics may be used.

The coil springs 38 are in a compressed state, thus axial forces act upon the cap 30 and the cup 40 which tend to move them apart. The cap 30 is secured to the lead tube 10 at the end 12. The flange 48 of the cup 40 is seated on the gasket 50 which is positioned adjacent to the upper casing 20. As a result of the forces produced by the coil springs 38, tensile stresses are placed on the lead tube 10 and compressive stresses are placed on the casings and 22 and the bushing support member 24. The compressive stresses maintain proper sealing surfaces between the bushing casings 20 and 22 and the bushing support member 24.

An expansion means is positioned between the cup flange 48 and the cap 30. In the embodiment shown in FIG. I, the expansion means comprises a suitably shaped gasket, such as the O-ring 54. Slots in the cap and in the cup flange 48 provide a space for proper seating of the O-ring 54. When the casing means, that is, the casings 20 and 22 and the bushing support member 24, changes its overall length by a different amount than the change in the length of the lead tube 10, the compressed lengths of the springs 38 change. This changes the separation distance between the flange 48 and the cap 30. Therefore, the O-ring 54 must expand or contract, depending on the direction of the change,

to maintain adequate sealing of the bushing.

In the embodiment shown in FIG. 2, the expansion means comprises a flexible band 56 constructed of a suitable material, such as semi-rigid metallic sheet. The upper edge 58 of the flexible band 56 is attached to the cap 30 by a suitable process, suchas brazing or soldering. The bottom edge 60 of the flexible band 56 is similarly attached to the cup flange 48. With this arrangement, a fluid-tightseal is provided by the flexible band, thus an O-ring as shown in FIG. 1 is not required. Al-

- though the flexible band 56 is shown in FIG. 2 closely following the contour of the cap 30, it is within the contemplation of this invention that the flexible band 56 may be shaped to provide a larger enclosed space and act as an oil expansion chamber.

Another embodiment of the invention is illustrated in FIG. 3. In this embodiment, the stress-relieving means 28 is positioned near the center portion of the bushing assembly. The bushing assembly is illustrated with an expansion chamber 62 positioned at the end 12 of the lead tube 10. However, it is within the contemplation of this invention that the bushing assembly may not include the expansion chamber 62.

The stress-relieving means 28' includes a circular channel 64 having channel sides 66 and 68 and a channel bottom 70. The channel sides 66 and 68 have sufficient spacing to permit telescoping of the circular channel 64 with the wall 72 of the bushing support member 24. A gasket 50' is positioned between the bottom and the upper casing 20 to provide a fluidtight seal. The compressed springs 38 are positioned in the circular channel 64 and exert forces on the channel bottom 70 and the bushing support member wall 72.

An expansion means provides a fluid-tight seal between the bushing support member 24 and the circular channel 64. The expansion means comprises a flexible band 74 having an upper edge 76 attached to the circular channel 64 and a lower edge 78 attached to the bushing support member 24. When the casing means and the lead tube 10 change lengths by different amounts, the circular channel 64 telescopes with respect to the bushing support member 24. Under these conditions, the band 74 flexes to permit telescoping while maintaining a fluid-tight seal.

In the embodiment shown in FIG. 4, the stressrelieving means 28" comprises a circular ring 80 having a slot 82 which telescopes with the bushing support member 24. An outer side 84 of the circular ring 80 surrounds the bushing support member 24 and an inner side 86 supports one end of the coil spring 38". The inner side 86 may not necessarily be continuous around the circular ring 80. It may only be projected from the circular ring 80 at positions where a spring 38" is located. As with the embodiment illustrated in FIG. 3, a difference in the expansion or contraction of the casing means and the lead tube 10 causes the circular ring 80 and the bushing support member 24 to telescope. The circular band 74 is attached to the circular ring 80 and to the bushing support member 24 to maintain a fluidtight seal therebetween similar to the arrangement described concerning the embodiment shown in FIG. 3.

The fact that the flange 26 of the bushing support member 24 may be attached to the enclosure of an electrical apparatus does not change the effects of different coefficients of thermal expansion. Normal variations in lengths between the lead tube 10 and the casing means over ordinary temperature ranges is on the order of one-fourth inch for large high-voltage bushings. With the larger space for placing the springs 38' and 38" provided by the embodiments shown in FIGS. 3 and 4, more coil springs may be placed around the lead tube 10. Thus, to achieve the same axial forces, more standard sized springs may be used in place of fewer heavy duty springs as taught by the prior art which results in a manufacturing cost improvement.

The bushing assemblies taught by this invention are physically smaller than prior art bushings and, therefore, are mechanically stronger. Since numerous changes may be made in the above-described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the acoompanying drawings shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. An electrical bushing assembly comprising a lead tube, casing means including an upper casing member concentrically positioned around said lead tube, a sub stantially circular cap having an opening therein into which said lead tube extends, a substantially circular cup having a bottom with an opening therein and a flange extending outwardly from said cup, compressed coil springs each having first and second ends, the first ends of said coil springs being adjacent to said circular cap, the second ends of said coil springs being adjacent to the bottom of said circular cup, the flange of said circular cup extending between said circular cap and said upper casing member, and an O-ring positioned between the flange and said cup and said cap.

2. An electrical bushing assembly comprising a lead tube, casing means including an upper casing member concentrically positioned around said lead tube, asubstantially circular bushing support member, a telescoping member positioned with a portion thereof located between said bushing support member and said upper casing member, compressed coil springs each having first and second ends, the first ends of said coil springs being adjacent to said bushing support member, the

second ends of said coil springs being adjacent to said second telescoping member, a flexible metallic band having first and second edges, the first edge of said band being attached to the telescoping member and the second edge of said band being attached to said bushtelescoping with the bushing support member.

a: a a: v =0: 

1. An electrical bushing assembly comprising a lead tube, casing means including an upper casing member concentrically positioned around said lead tube, a substantially circular cap having an opening therein into which said lead tube extends, a substantially circular cup having a bottom with an opening therein and a flange extending outwardly from said cup, compressed coil springs each having first and second ends, the first ends of said coil springs being adjacent to said circular cap, the second ends of said coil springs being adjacent to the bottom of said circular cup, the flange of said circular cup extending between said circular cap and said upper casing member, and an O-ring positioned between the flange and said cup and said cap.
 2. An electrical bushing assembly comprising a lead tube, casing means including an upper casing member concentrically positioned around said lead tube, a substantially circular bushing support member, a telescoping member positioned with a portion thereof located between said bushing support member and said upper casing member, compressed coil springs each having first and second ends, the first ends of said coil springs being adjacent to said bushing support member, the second ends of said coil springs being adjacent to said sEcond telescoping member, a flexible metallic band having first and second edges, the first edge of said band being attached to the telescoping member and the second edge of said band being attached to said bushing support member, said flexible band being positioned substantially around the outside of said telescoping member.
 3. The electrical bushing assembly of claim 2 wherein the telescoping member comprises a substantially circular channel having channel sides and a bottom portion, said channel sides having a sufficient separation distance to permit telescoping of said circular channel with the bushing support member.
 4. The electrical bushing assembly of claim 2 wherein the telescoping member comprises a circular ring having inner and outer sides which form a slot therebetween, said slot having sufficient dimensions to permit telescoping with the bushing support member. 